The present invention relates to a method for prioritised data transmission to a common transmission medium of a plurality of interface modules coupled to it, and interfacing at least one input bitstream with the common transmission medium, each interface module of the plurality having a module priority on the basis of which access to said common transmission medium is arbitrated during a grant cycle. The invention also relates to a data transmission arrangement including a plurality of interface modules, for interfacing at least one input bitstream with a common transmission medium, each interface module including at least one storage queue adapted to store packets of the at least one input bitstream prior to accessing the common transmission medium, the each interface module having a respective module priority on the basis of which access to the common transmission medium is arbitrated during a grant cycle, and which is determined by an interface module priority means included in the each interface module.
A data transmission arrangement for performing such a method is already known in the art, e.g. from the Published European patent application, publication number EP 0584405 A1, entitled: xe2x80x9cData transmission system and interface module and priority generation means included thereinxe2x80x9d. Therein, a data transmission system or arrangement, including a plurality of interface modules, interfacing a plurality of input bitstreams with a common transmission medium, is described, wherein each interface module includes storage means, each including storage registers or storage queues, adapted to store packets of said input bitstreams prior to accessing said common transmission medium. Each of the interface modules described in the prior art document additionally includes packet priority determining means adapted for generating, for each of the packets stored in said storage means, a packet priority as a function of its storage time in said storage means and of at least one packet characterising parameter. Each interface module of the prior art data transmission arrangement is further granted access to the common transmission medium, based on an interface module priority, which is itself determined from the individual packet priority values associated to the individual packets stored within this interface module.
In case the input bitstream consists of an ATM input bitstream, the prior art method and arrangement does however not provide for prioritised access between different ATM service categories, to which individual packets of this bitstream are associated. Indeed, in the prior art method and arrangement, the interface module priority on the basis of which the prioritised access is granted, and determined from the packet priority of the packets of the bitstreams, is merely dependent upon the storage time of these packets in the storage queue, and upon at least one packet characterising parameter. Some examples of such a packet characterising parameter are referenced in the prior art document as being the packetising delay during the packetising process in the packetising means, described in the prior art document, or as related to the type of information contained in the packets, for example to make a distinction between data and voice. No reference is however made to a connection parameter. Since the ATM service category is however determined by a combination of both Quality of Service parameters such as cell delay variation, cell transfer delay and cell loss ratio, and traffic parameters such as peak cell rate, sustainable cell rate maximum burst size, and minimum cell rate, all of which are not parameters inherently characterising the packet itself, but characterising the connection associated to part of the input bitstream of which the packet forms part, the referenced prior art method is not adapted for providing access amongst a number of competing ATM service category bitstreams, entering at least one interface module, to the common transmission medium.
An object of the present invention is thus to provide a method and data transmission arrangement for realising prioritised data transmission between different ATM service categories.
According to the invention, this object is achieved by letting at least one interface module priority to be dependent upon at least one connection parameter.
Such an object is achieved by a method for prioritised data transmission to a common transmission medium of a plurality of interface modules coupled to it, and interfacing at least one input bitstream with the common transmission medium, each interface module of the plurality having a module priority on the basis of which access to the common transmission medium is arbitrated during a grant cycle, wherein for at least one interface module amongst the plurality, the module priority is dependent on at least one connection parameter associated to packets of the at least one input bitstream.
This object is also achieved by a data transmission arrangement including a plurality of interface modules, for interfacing at least one input bitstream with a common transmission medium, each interface module including at least one storage queue adapted to store packets of the at least one input bitstream, prior to accessing the common transmission medium, each interface module having a respective module priority on the basis of which access to the common transmission medium is arbitrated during a grant cycle, and which is determined by an interface module priority means included in the each interface module, wherein, for at least one interface module amongst the plurality, the module priority is dependent on at least one connection parameter associated to the packets of the at least one input bitstream.
Indeed, since the value of one or a combination of the values of these connection parameters is directly related to a specific ATM service category, and since the interface module priority is now determined by at least one of these connection parameters, the access arbitration, based on interface module priorities is now adapted to differentiate between different ATM service categories.
An additional characteristic feature of the present invention is that said method further includes a first step of routing at least part of the packets of the at least one input bitstream into at least one storage queue of the at least one interface module, based on the values of the at least one connection parameter, whereby each distinct storage queue amongst the at least one storage queue corresponds to a distinct predetermined combination of values of the at least one connection parameter, whereby for the each distinct storage queue, a distinct queue priority associated to the each distinct storage queue is determined, from which the interface module priority of the at least one interface module is further determined and that said data transmission arrangement is further adapted where the data transmission arrangement further includes routing means, adapted to route at least part of the packets of the at least one input bitstream towards the at least one storage queue included in the at least one interface module, based on the value of the at least one connection parameter, whereby each distinct storage queue amongst the at least one storage queue of the at least one interface module corresponds to a distinct predetermined combination of values of the at least one connection parameter, and is further associated to a distinct queue priority determining means included in the at least one interface module and being adapted to calculate a distinct queue priority associated to each distinct storage queue, whereby the interface module priority means of the at least one interface module is further adapted to determine the interface module priority from each of the distinct queue priorities associated to the each distinct storage queue of the at least one interface module.
As a result of this, by associating specific storage queues to specific ATM service categories, as is obtained by the correspondence of each storage queue to a distinct predetermined combination of values of said at least one connection parameter, and by determining a distinct queue priority per specific storage queue from which the interface module priority is determined, a simple implementation of the above mentioned principle is obtained.
A further characteristic feature of the present invention in case the at least one storage queue consists of one storage queue the interface module priority corresponds to the queue priority associated to the one storage queue; and wherein the data transmission apparatus has a corresponding apparatus feature.
Thereby, in case the interface modules only include one storage queue, the obtained queue priorities directly correspond to the interface module priorities. In this special case each interface module in fact only receives data associated to one specific ATM service category, as will be explained more into detail in a further paragraph.
Still another characteristic feature of the present invention for the each distinct storage queue, the distinct queue priority is selected from a distinct predetermined set of values; and wherein the data transmission apparatus has a corresponding apparatus feature.
In this way, priority differentiation amongst the different ATM service categories is obtained by selecting the queue priorities associated to these different ATM service categories, from distinct predetermined sets of values.
Yet a further characteristic feature of the present invention is the distinct predetermined sets of values, related to the distinct storage queues are non-overlapping; and wherein the data transmission apparatus has a corresponding apparatus feature.
By letting these distinct predetermined sets of values to be non-overlapping sets, the aforementioned differentiation is even more pronounced. In addition, the connection admission control function, although not being subject of this present invention, but being an essential part of the network of which this data transmission arrangement of the present invention forms part, is seriously simplified.
Another characteristic feature of the present invention is for at least one specific storage queue amongst the at least one storage queue, the queue priority associated to the at least one specific storage queue, is adapted at predetermined instances; and wherein the data transmission apparatus has a corresponding apparatus feature.
Thereby, by adapting the priority of a particular storage queue at predetermined instances, the possibility of guaranteeing a minimum cell rate is foreseen. This is especially valuable for these specific ATM service classes for which no total bit rate is specified, such as the available bit rate category. By, at predetermined instances temporarily increasing the associated queue priority, leading to an increased probability of gaining the access, yet a minimum transmission of cells of this service category is provided.
Yet a further characteristic feature of the present invention is the predetermined instances are related to the at least one specific storage queue; and wherein the data transmission apparatus has a corresponding apparatus feature.
In this way a further differentiation, but now between these specific ATM service classes for which the total bit rate is not specified such as for instance the available bit rate and the unspecified bit rate class, is provided, enabling to favour some of these categories with respect to others.
Yet another characteristic feature of the present invention is the predetermined instances are further related to a predetermined amount of calls to be transmitted from the at least one specific storage queue; and wherein the data transmission apparatus has a corresponding apparatus feature.
Thereby, by further relating the predetermined instances at which the priority of the specific ATM service categories is adapted, to predetermined amounts of cells to be transmitted from the associated storage queue, yet a fine tuning of the minimum guaranteed cell rate in these categories is provided. This results in even a more versatile method and arrangement.
Still a further characteristic feature of the present invention is the respective queue priority associated to the at least one specific storage queue, is alternatively selected, at the predetermined instances from at least two predetermined sets of values, each of which is related to the at least one respective storage queue; and wherein the data transmission apparatus has a corresponding apparatus feature.
In this way, a simple, low cost, implementation of the temporary varying priority for these specific ATM service categories is obtained.
Still another characteristic feature of the present invention is for the at least one specific storage queue, the at least two predetermined sets of values are non-overlapping; and wherein the data transmission apparatus has a corresponding apparatus feature.
As a result, a clear and marked differentiation between the temporarily varying priority values of these specific ATM service categories is obtained. By further combining this with the principle described in claims 5 and 18, all priority values related to all distinct ATM service categories, are distinctly marked.
Yet another characteristic feature of the present invention is for the method being applicable to a first interface module and a second interface module of the plurality, each respectively including a first, respectively a second, distinct storage queue with an associated first, respectively second, distinct queue priority, with the first distinct storage queue and the second distinct storage queue being related to the same predetermined combination of values of the at least one connection parameter, the first distinct queue priority and the second distinct queue priority are adaptable after each grant cycle; and wherein the data transmission apparatus has a corresponding apparatus feature.
This feature is especially important for guaranteeing fairness amongst identical ATM service categories, but attributed to packets entering and stored in different interface modules. By letting the priorities of the associated queues, to be adaptable after each grant cycle, fairness amongst the different competing interface modules is now obtained.
In this way, a simple method for implementing this fairness amongst different interface modules, is realised.